Braking or clutching device

ABSTRACT

An electric braking or clutching device includes a housing; an armature having an axis and disposed at the housing, the armature and the housing defining a radial air gap therebetween; and a coil configured to generate, when energized, a magnetic field at the housing and armature, a flux path of the field extending from the coil into the housing, from the housing into the armature, from the armature into the housing, and from the housing back to the coil, with the direction of the flux path from the armature into the housing being substantially radial in orientation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/742,185, which was filed Apr. 30, 2007 and which is incorporated byreference herein in its entirety, that application itself being acontinuation-in-part of U.S. application Ser. No. 11/415,263, filed May1, 2006, which is also incorporated by reference herein in its entirety.

BACKGROUND

Devices used for braking or clutching are common in industry. It isoften desirable to selectively control speed or torque of a rotatablecomponent of a device or to selectively engage a rotatable component.Such devices are utilized in industry for many and varied applicationsincluding actuators in assembly lines, automated systems, etc.

Currently, braking and clutching duties are handled by devices includingmagnetorheological fluid based devices and spring-based devices. Whilecommercially available devices generally operate as marketed and areeffective for some applications, they are expensive, lack adjustability,or both.

Since greater economy and adjustability are always desirable,improvements are always well received.

SUMMARY OF THE INVENTION

An electric braking or clutching device includes a housing; an armaturehaving an axis and disposed at the housing, the armature and the housingdefining a radial air gap therebetween; and a coil configured togenerate, when energized, a magnetic field at the housing and armature,a flux path of the field extending from the coil into the housing, fromthe housing into the armature, from the armature into the housing, andfrom the housing back to the coil, with the direction of the flux pathfrom the armature into the housing being substantially radial inorientation.

A braking or clutching device includes a first plurality of discsrotationally fixed to one of a housing or a shaft; and at least onesecond disc interengaged with the first plurality of discs androtationally fixed to the other of the housing or the shaft, at leastone of the first plurality of discs and the at least one second discpresenting a contact surface, for contact with another of the firstplurality of discs and at least one second disc, the surface comprisinga low friction bearing material having a kinetic coefficient of frictionsubstantially the same as its static coefficient of friction.

A magnetically actuable device includes a housing; and an armaturedisposed at the housing and axially movable relative to the housing, thedevice having a substantially uniform magnetic actuation forcesustainable through a majority of an axial movement of the deviceirrespective of wear of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, willbecome readily apparent to those skilled in the art from the followingdetailed description of a preferred embodiment when considered in thelight of the accompanying drawings in which:

FIG. 1 is a cross section view of a selective engagement device;

FIG. 1 a is a plan view of the device illustrating the section line forFIG. 1;

FIG. 2 is a perspective view of a shaft of the device;

FIG. 3 is a perspective view of an armature of the device;

FIG. 4 is a perspective view of a housing of the device;

FIG. 5 is a plan view of a thrust washer of the device;

FIG. 6 is a plan view of a friction disk of the device; and

FIG. 7 is an enlarged view of circumscribed area 7-7 in FIG. 1.

FIG. 8 is the view of FIG. 7 with the flux path illustrated by a heavyblack line.

DETAILED DESCRIPTION OF THE DRAWINGS

Prior to discussing the figures, it is important to point out thatalthough the drawings and description hereof are directed to a devicewhere the housing is outwardly adjacent the armature, the conceptsdisclosed herein are applicable to the housing being inwardly adjacentthe armature. The armature may also be adjacent the housing in asideways manner. Referring to FIG. 1, a selective engagement device 10is generally depicted in cross section. It is important to note that thesection line as depicted is not a diametral line but rather is thatillustrated in figure la. The device includes a coil housing 12 andcover 14. Supported within the coil housing 12 and cover 14 are a rotaryshaft 16 supported by bearings 18, 20 and 22. A retention ring 24 ispositionable in a groove 26 adjacent to bearing 22 while retention ring28 is positioned in groove 30 adjacent bearing 18 to retain the shaft 16in its desired position relative to the housing 12 and cover 14. Furtherprovided is a seal 32 to maintain the environment internal to housing 12and cover 14.

A plurality of friction disks 34 (a circular limitation is not intendedby the term “disk” but rather any desired perimetrical shape may beused) is positioned, in alternating manner, with a plurality of thrustwashers 36. In the illustrated embodiment, there are shown two frictiondisks and three thrust washers. It will be understood however that thenumber of disks and thrust washers is not limited to that shown but thatmore or fewer could be utilized in particular applications, evenincluding none. If none is desired, then in one embodiment the housingsurface facing the armature and the armature surface opposing theidentified housing surface will be hardened or otherwise treated toprolong wear resistance. Returning to the illustrated embodiment, thefriction disks 34 are driven by (or drive through) shaft 16 in oneembodiment through the use of a hexagonal opening 38 (see FIG. 6)complimentary to a hexagonal drive profile 40 (see FIG. 2) on shaft 16.It is to be appreciated that while a hexagonal drive shape has beenemployed in the embodiment illustrated, any geometric shape havingsufficient drive capability for the application is substitutable for thehexagonal shape. This includes a splined connection, should one bedesirable. Functionality is provided by the disks being driven at theaxis thereof as will become more apparent hereinafter. The plurality ofthrust washers 36, on the other hand are configured to clear driveprofile 40 with an opening 42 that is simply large enough to not engagewhatever geometric profile is utilized for profile 40 (see FIG. 4), thepoint in this instance being that the thrust washers are to be rotatablerelative to the shaft and friction disks or the shaft (and frictionsdisks) be rotatable relative to the washers. The thrust washers 36include engagement tabs 44, which in one embodiment number four, evenlyspaced around each thrust washer 36. Tabs 44 are intended to be engagedby at least one recess 46 in an armature 48 (see FIG. 3, four shown).The tabs engaged with recesses 46 prevent relative rotational motionbetween the washers and the armature.

Armature 48 includes a bearing opening 50 in which bearing 18 isreceived to support armature 48, although it is to be understood thatthe bearing depicted is optional and existing in the illustratedembodiment but could be eliminated in alternate embodiments withouteffect on operation of the device as herein disclosed. Armature 48 isaxially displaceable along bearing 18 such that it may be actuatedagainst the thrust washers and friction disks when it is desired to slowor stop relative rotation between shaft 16 and the housing and cover 12,14. In one embodiment, it is necessary that the armature not haverelative rotational motion capability with respect to the housing 12.Thus, as illustrated in FIG. 3, armature 48 is provided with engagementrisers 52. Four risers 52 are illustrated although more or fewer couldbe used. In the illustrated embodiment, using four risers 52 and fourrecesses 46 maintains annular thickness of the armature 48.

Referring to FIGS. 5 and 6, the disks 34 and washers 36 are illustratedapart from other structures. The washer tabs 44 as noted are intended toengage in recesses 46 for a non-rotational engagement with armature 48.To complete the nonrotational engagement from the washers 36 to housing12, the risers 52 engage grooves 54 (illustrated in FIG. 4). With thisarrangement, the washers 36 are substantially rotationally immobilerelative to the housing 12, which facilitates the purpose of the device.It will be understood that this is but one possibility of an arrangementfor antirotation between the washers and armature, others functionallyequivalent are substitutable as desired.

With the washers 36 immobile and the friction disks 34 sandwichedbetween the washers 36 (and configured to rotate with the shaft 16) thefriction disks must slide past the washers 36. Because of thisarrangement, if a compressive load is applied to the washers/disks, theeffective total friction rises and relative motion between the washersand disks reduces or stops. Such inhibition of relative motion may beused for braking or clutching in various applications. The impetus forthe compressive load in the depicted embodiment is an electromagneticattractive force generated between the housing 12 and the armature 48.It is noted here that a specific relationship for the armature andhousing is disclosed herein that causes a flux path of the device to beunique and as a consequence causes the air gap between the housing andarmature to remain constant throughout the service life of the deviceirrespective of wear of the device and without need for adjustment ofany kind. This will be detailed hereunder.

A coil 56, as illustrated in FIG. 1, generates the electromagneticforce. The coil 56 is cradled in a bobbin 58 disposed within housing 12.One lead 60 (of two, the other not being visible in this view),electrically connected to the coil 56 is illustrated in FIG. 1 forclarity. Coil 56 becomes magnetically active when a current is appliedthereto. The magnetic properties of coil 56 are utilized to drawarmature 48 towards the coil 56 thereby compressing thrust washers 36and friction disks 34 between an inside surface 62 of armature 48 and ahousing surface 64. Compression of washers 36 and disks 34 createssignificant friction to be utilized in retarding relative rotationbetween shaft 16 and housing 12, as noted above. The device disclosedherein provides for a significantly longer life than prior art devicesas it is capable of about forty-thousandths to about fifty-thousandthsof an inch of wear in the friction generating members before losingselective braking or clutching power whereas the prior art is merelycapable of ten thousandths of an inch of wear. The inventionaccomplishes this desirable result by causing the magnetic flux path ofthe device to flow from coil 56 to armature 48 and then to the housingin a direction substantially radial in orientation rather than axially(of the device) through the air gap between the housing and armature.This is contrary to what clutching and braking devices have done in thepast. The creation of the radial flux path is occasioned by the additionto the armature 48 of a portion thereof radially concentricallypositioned relative to a portion of the housing, such as a ring ofmaterial 66 positioned to extend from a planar portion 68 of armature 48into an annular space 70 within which bobbin 58 and coil 56 aredisposed. The ring 66, because it extends into the space 70 by a smallamount, while providing a radial air gap 72 between the housing 12 andthe armature 48, physically causes the flux path to flow substantiallyradially as opposed to axially from the armature 48 to the housing 12,as it does in the prior art. The arrangement provides for a lower totalmagnetic force on the armature but one that is consistent over a longerrange. More specifically, the device exhibits a substantially uniformmagnetic actuation force sustainable through a majority of an axialmovement of the device irrespective of wear of the device. Statedalternately, the prior art suffers a reduction in the magnetic actuationforce as the discs and washers wear due to ordinary use of the device.In the present invention, the wear of these items does not affect themagnetic actuation force to any appreciable degree. This is whatprovides the benefit of the greater wear tolerance in the presentarrangement. It is the air gap 72 between the housing 12 and thearmature 48, because it is radially oriented that is responsible for thebenefit. The air gap is not in a wear path of the device (the wear pathbeing axial due to frictional wear of the disks and washers in an axialdirection). The gap 72 therefore does not change in dimension butremains consistent regardless of the wear in the friction disks 34.Prevention of change in the dimension of the air gap 72 through whichthe flux passes contributes to the steady force generated over the lifeof the device (e.g. between about 0.020 inch and 0.070 inch of axialwear in the device. Referring to FIG. 7, an enlarged view of a portionof FIG. 1 allows for illustration of the air gap 72. The flux paththrough the air gap is illustrated in FIG. 8 by a heavy black line 74.

Providing further benefit to the devices disclosed herein is theadditional teaching hereof that the disks and washers in a clutching orbraking system may be constructed at least partially of torque transfermaterials having a kinetic coefficient of friction substantially thesame as its static coefficient of friction or within about plus or minus5 percent of 1:1. It is to be understood however that although benefitof the invention diminishes with increasing disparity between thekinetic coefficient of friction and the static coefficient of friction,benefits hereof are still largely exhibited up to about 20 percentdifference. In one embodiment, the material is a bearing material ofnylon with a PTFE (Polytetrafluoroethylene) or other low frictionadditive and exhibits a ratio of static coefficient of friction tokinetic coefficient of friction of about 1.05. It is further to be notedthat while the foregoing disclosure relates in large part to anelectromagnetic device, the utilization of a torque transfer materialhaving the stated range of ratio of static to kinetic coefficient offriction is not restricted to electrically or magnetically actuabledevices but may be employed in any clutching or braking device fortorque transfer. This includes but is not limited to hydraulicallyactuable devices, mechanically actuable devices pneumatically actuabledevices, etc. The property as stated, and as is implied by the statementitself, means that there is very little “stick-slip” action in thesystem of the invention. As an astute reader might posit, suchproperties also indicate a relatively low production of usable friction.While this condition might be considered questionable for aclutching/braking device, the benefits of avoidance of “stick-slip” aremore important. This is especially the case in view of the fact that theloss in overall friction in the system can be easily compensated for byincreasing the radial distance from the axis of the device to thefriction surface, increasing the frictional area, or increasing thenumber of frictional interfaces (disks and washers) in the system. It isalso contemplated to use more than one of these compensatingarrangements together in some applications.

The device as detailed hereinabove provides not only for greater weartolerance in use but also allows for selectivity in the amount ofbraking force or clutching engagement it will impart to a particularsystem. This benefit is occasioned by the fact that the device isultimately controlled by the amount of current put to the coil 56. Thegreater the current applied to the coil, the greater the magnetic fieldgenerated thereby. The greater the magnetic field the stronger the pullon the armature, and consequently the greater the compression of thefriction disks. The amount of friction generated between the thrustwashers and friction disks therefore can be varied as a function of theapplied current.

It is noted that the above-described embodiment is one possibleembodiment utilizing the radial air gap and flux path disclosed. Itshould also be appreciated however that the essential features of thisconcept, i.e. braking or clutching can also be carried out using theradial air gap and flux path but without utilizing friction disks orthrust washers. In such embodiment, the armature would be rotatablerelative to the housing when the coil was not energized and would bepulled into frictional contact with the housing when the coil isenergized. This would promote wear of the housing and the armature butwith suitable selection of materials, the device would work acceptably.

It is to be understood that the braking or clutching device as disclosedherein is not limited to industrial applications. Rather the device isuseful for many different applications where selectively actuably torquetransfer is desirable or useful. These include arrangements such as ahuman tactile interface arrangements, responsive to a control algorithm,employed in devices such as video games where tactile feedback is usefulto enhance the gaming experience. Moreover, the torque transfer devicesdisclosed herein are useful in steer by wire applications in order toprovide tactile feedback to a pilot of a plane, boat or motor vehicle.Further the devices disclosed herein are useful for tensioning systemswhere a sensor system is configured to sense tension in, for example, aweb and provide sensory information to a controller that then actuates abraking of clutching device provided in the system to modify the tensionin the web. Yet still the devices disclosed herein are useful invariable torque proportioning devices, etc. In short, the devices asdisclosed herein are applicable to any system wherein control overtorque transfer is useful.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustration and not limitation.

1. A braking/clutching device providing a tactile operating sensationfree of stick-slip action, the device comprising: a housing having alongitudinal axis; a generally annular movable member mounted in thehousing for movement in a direction generally along the longitudinalaxis of the housing; a shaft mounted in the housing for rotationrelative to the housing and the movable member, and adapted to berotated by manual operation of a human operator; a first diskrotationally fixed relative to one of the housing or the shaft but freeto move longitudinally with respect thereto; and a second diskrotationally fixed relative to the other of the housing or the shaft butfree to move longitudinally with respect thereto, a force applicationdevice in the housing selectively applying force to the movable memberfor moving the movable member longitudinally within the housing, withthe first and second disks being held in frictional sliding engagement,with the amount of force holding the disks together being a function ofthe level of force applied to the movable member by the forceapplication device; the first and second disks presenting a contactsurface comprising a bearing material having a relatively lowcoefficient of friction and a kinetic coefficient of friction that issubstantially the same as its static coefficient of friction; and withthe braking/clutching device providing a tactile sensation free ofstick-slip action when the sets of disks are held in frictional slidingengagement and the shaft is rotated within the housing away from astationary position.
 2. The braking/clutching device of claim 1, whereinthe value of the kinetic coefficient of friction and the value of thestatic coefficient of friction are within 20% of each other.
 3. Thebraking/clutching device of claim 1, wherein the value of the kineticcoefficient of friction and the value of the static coefficient offriction are within 5% of each other.
 4. The braking/clutching device ofclaim 1, wherein the contact surfaces comprise nylon with apolytetrafluoroethylene additive.
 5. The braking/clutching device ofclaim 1, further comprising a first set of 2 or more of said firstdisks.
 6. The braking/clutching device of claim 1, further comprising asecond set of 2 or more of said disks.
 7. The braking/clutching deviceof claim 1, wherein the force application device is selected from agroup comprising an electrically actuated device, a pneumaticallyactuated device, a hydraulically actuated device and a mechanicallyactuated device.
 8. The braking/clutching device of claim 1, wherein theforce application device is a coil of electric conductor for selectivelygenerating a magnetic field and the movable member is an armaturemovable under the application of a magnetic field.
 9. Thebraking/clutching device of claim 1, wherein one of the disks is mountedto and carried in an interior recess of the movable member and themovable member is rotationally fixed relative to the housing.
 10. Thebraking/clutch device of claim 1, wherein the contact surface ispresented by an engaging surface of each of the disks.
 11. Abraking/clutching device, comprising: a movable member and a rotatableshaft mounted in a housing, the movable member being movable in a lineardirection and rotationally fixed relative to the housing and the shaftbeing rotatable relative to the housing; a first disk movable in thelinear direction, rotationally fixed relative to the housing androtatable relative to the shaft; a second disk movable in the lineardirection, rotationally fixed relative to the shaft and rotatablerelative to the housing; and a device disposed to selectively move themovable member in the linear direction to thereby bring respectivecontact surfaces of the disks into frictional engagement, bearingmaterials of the contact surfaces each having relatively low and similarkinetic and static coefficients of friction such that a tactilesensation free of stick-slip action is provided to an operator duringthe frictional engagement when the shaft is rotated by the operator. 12.A tactile feedback interface arrangement including an electric brakingand clutching device to impart tactile feedback, the arrangementcomprising: a housing; an armature mounted for axial movement relativeto the housing; a shaft extending through and rotatably mounted in thehousing and the armature for rotation relative to the housing andarmature; a first set of disks rotationally fixed to one of the armatureor the shaft and free to move longitudinally with respect thereto; and asecond set of disks, interleaved with the first set of disks,rotationally fixed to the other of the armature or the shaft and free tomove longitudinally with respect thereto, the first and the second setsof disks presenting contact surfaces comprising a bearing materialhaving a relatively low coefficient of friction and kinetic and staticcoefficients of friction that are within about five percent of oneanother to avoid a tactile sensation of stick-slip action when anoperator rotates the shaft with the sets of disks being pressed togetherby the movement of the armature.